U.S. patent number 7,543,670 [Application Number 11/263,215] was granted by the patent office on 2009-06-09 for wheel slip control system.
This patent grant is currently assigned to GM Global Technology Operations, Inc.. Invention is credited to Birendra P. Bhattarai, Goro Tamai, James L. Worthing.
United States Patent |
7,543,670 |
Tamai , et al. |
June 9, 2009 |
Wheel slip control system
Abstract
A wheel slip control system includes wheel speed sensors that
generate wheel speed signals and a control module that controls
torque production of at least one of an engine and an electric
motor and that detects a negative wheel slip based on the wheel
speed signals. The control module increases torque production of at
least one of the engine and the electric motor when the negative
wheel slip is detected.
Inventors: |
Tamai; Goro (West Bloomfield,
MI), Worthing; James L. (Munith, MI), Bhattarai; Birendra
P. (Novi, MI) |
Assignee: |
GM Global Technology Operations,
Inc. (Detroit, MI)
|
Family
ID: |
37989699 |
Appl.
No.: |
11/263,215 |
Filed: |
October 31, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070095589 A1 |
May 3, 2007 |
|
Current U.S.
Class: |
180/197;
180/244 |
Current CPC
Class: |
B60K
6/48 (20130101); B60W 30/18172 (20130101); B60W
10/30 (20130101); B60W 20/15 (20160101); B60W
10/08 (20130101); B60K 28/16 (20130101); B60W
10/06 (20130101); B60L 2240/441 (20130101); F16H
2059/467 (20130101); B60W 2520/26 (20130101); Y02T
10/6286 (20130101); Y02T 10/62 (20130101); B60W
20/00 (20130101); B60W 2710/0666 (20130101); B60W
2510/0638 (20130101); B60W 2710/083 (20130101); Y02T
10/6221 (20130101) |
Current International
Class: |
B60K
28/16 (20060101) |
Field of
Search: |
;180/197 ;477/35 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Dickson; Paul N
Assistant Examiner: Adams; Tashiana
Claims
What is claimed is:
1. A wheel slip control system for a vehicle, said wheel slip
control system comprising: wheel speed sensors that generate wheel
speed signals; and a control module that controls torque production
of at least one of an engine and an electric motor and that detects
a negative wheel slip based on said wheel speed signals when at
least one of said engine and said electric motor are back driven;
wherein said control module increases torque production of at least
one of said engine and said electric motor when said negative wheel
slip is detected.
2. The wheel slip control system of claim 1, said vehicle having an
air conditioner, wherein said control module regulates a compressor
capacity of said air conditioner and decreases said compressor
capacity when said negative wheel slip is detected.
3. The wheel slip control system of claim 1, said vehicle having an
air conditioner, wherein said control module regulates a rotational
speed of a compressor of said air conditioner and decreases said
rotational speed when said negative wheel slip is detected.
4. The wheel slip control system of claim 1, said vehicle having a
torque converter and a transmission, further comprising: a torque
converter clutch slip sensor that generates a torque converter
clutch slip signal; and an engine rotational speed sensor that
generates an engine rotational speed signal; wherein said control
module calculates axle torque based on said torque converter clutch
slip signal, said engine rotational speed signal, and said wheel
speed signals, and increases torque production of at least one of
said engine and said electric motor when said calculated axle
torque is negative.
5. The wheel slip control system of claim 4, said vehicle having an
air conditioner compressor, wherein said control module calculates
said axle torque based on one of an air conditioner compressor
capacity and an air conditioner compressor rotational speed.
6. The wheel slip control system of claim 1, wherein said control
module increases torque production of said engine by activating a
first cylinder of said engine, waiting a predetermined number of
engine cycles, and activating a second cylinder of said engine.
7. The wheel slip control system of claim 1, wherein said control
module detects a positive wheel slip based on said wheel speed
signals and disables at least one fuel efficiency function of said
vehicle when said positive wheel slip is detected.
8. The wheel slip control system of claim 7, wherein said at least
one fuel efficiency function comprises at least one of a
deceleration fuel deactivation function and an idle stop
function.
9. A wheel slip control system for a vehicle having an engine, said
wheel slip control system comprising: wheel speed sensors that
generate wheel speed signals; and a control module that controls
torque production of said engine, that detects a negative wheel
slip based on said wheel speed signals when said engine is back
driven, and that calculates axle torque based on said wheel speed
signals; wherein said control module increases torque production of
said engine when said negative wheel slip is detected and when said
calculated axle torque is negative.
10. The wheel slip control system of claim 9, wherein said control
module increases torque production of said engine by activating a
first cylinder of said engine, waiting a predetermined number of
engine cycles, and activating a second cylinder of said engine.
11. The wheel slip control system of claim 9 wherein said control
module increases torque production of said engine by decreasing a
spark offset of an ignition system of said engine.
12. The wheel slip control system of claim 9 wherein said control
module detects a positive wheel slip based on said wheel speed
signals, and disables at least one fuel efficiency function of said
vehicle when said positive wheel slip is detected.
13. The wheel slip control system of claim 12, wherein said at
least one fuel efficiency function comprises at least one of a
deceleration fuel deactivation function and an idle stop
function.
14. A method for controlling wheel slip in a vehicle having an
engine, said method comprising: detecting a negative wheel slip
when said engine is back driven; calculating an axle torque;
increasing torque production of said engine when said negative
wheel slip is detected and when said calculated axle torque is
negative.
15. The method of claim 14 further comprising: decreasing at least
one of an air conditioner compressor capacity and an air
conditioner compressor rotational speed when said negative wheel
slip is detected and when said calculated axle torque is
negative.
16. The method of claim 14, said vehicle having an electric motor
coupled with an energy storage device, said method further
comprising: recharging said energy storage device with current from
said electric motor when said vehicle is decelerating; and
decreasing said current when said negative wheel slip is detected
and when said calculated axle torque is negative.
17. The method of claim 14, said vehicle having an electric motor,
said method further comprising: increasing torque production of
said electric motor when said negative wheel slip is detected and
when said calculated axle torque is negative.
18. The method of claim 14, wherein said increasing torque
production of said engine comprises activating fuel delivery to a
first cylinder of said engine, waiting a predetermined number of
engine cycles, and activating fuel delivery to a second cylinder of
said engine.
19. The method of claim 14, wherein said increasing torque
production of said engine comprises decreasing a spark offset of an
ignition system of said engine.
20. The method of claim 14 further comprising: detecting a positive
wheel slip; and disabling at least one of a deceleration fuel
deactivation function and an idle stop fuel deactivation function
when said positive wheel slip is detected.
Description
FIELD OF THE INVENTION
The present invention relates to vehicle control systems, and more
particularly to a wheel slip control system.
BACKGROUND OF THE INVENTION
To improve fuel economy, fuel delivery to an engine in a hybrid or
conventional powertrain vehicle may be deactivated during vehicle
deceleration and vehicle stops. During deceleration, the engine,
electric motor/generator (EMG), and air conditioner (AC) may be
back driven by the vehicle wheels. When fuel delivery to the engine
is deactivated, the EMG may recharge an energy storage device
(ESD). The drag of the engine, EMG, and AC may result in increased
negative drive-axle torque. Negative wheel slip may occur when the
force required to back drive the engine, EMG, and AC becomes
greater than the frictional force between the road and the driven
wheels.
Positive wheel slip may occur when the operator aggressively drives
the vehicle. When the vehicle is accelerated, the force of the
positive drive-axle torque may become greater than the frictional
force between the road and the drive wheels. In such case, positive
wheel slip occurs. When aggressively driving the vehicle, the
operator may disable the vehicle traction control system.
Traditionally, wheel slip is detected by the anti-lock braking
system (ABS) and by the traction control system. In the traditional
system, however, wheel slip is not controlled when the brakes are
not applied or when the traction control system is disabled.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a wheel slip control
system. The wheel slip control system includes wheel speed sensors
that generate wheel speed signals. A control module controls torque
production of at least one of an engine and an electric motor and
detects negative wheel slip based on the wheel speed signals. The
control module increases torque production of at least one of the
engine and the electric motor when negative wheel slip is
detected.
In one feature, the control module regulates a compressor capacity
of an air conditioner, and decreases the compressor capacity when a
negative wheel slip is detected.
In other features, the wheel slip control system includes a torque
converter clutch slip sensor that generates a torque converter
clutch slip signal and an engine rotational speed sensor that
generates an engine rotational speed signal. The control module
calculates axle torque based on the torque converter clutch slip
signal, the engine rotational speed signal and the wheel speed
signals, and increases torque production of at least one of the
engine and the electric motor when the calculated axle torque is
negative.
Further areas of applicability of the present invention will become
apparent from the detailed description provided hereinafter. It
should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the
detailed description and the accompanying drawings, wherein:
FIG. 1 is a schematic illustration of an exemplary hybrid vehicle
according to the present invention;
FIG. 2 is a flowchart illustrating steps performed by a wheel slip
control system according to the present invention;
FIG. 3 is a flowchart illustrating steps performed to control
torque;
FIG. 4 is a flowchart illustrating steps performed to disable fuel
efficiency functions; and
FIG. 5 is a flowchart illustrating steps performed to enable fuel
efficiency functions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely
exemplary in nature and is in no way intended to limit the
invention, its application, or uses. For purposes of clarity, the
same reference numbers will be used in the drawings to identify
similar elements. As used herein, the term module refers to an
application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that
execute one or more software or firmware programs, a combinational
logic circuit, and/or other suitable components that provide the
described functionality.
Referring now to FIG. 1, a wheel slip control system 10 for a
hybrid vehicle is shown. As can be appreciated, the control system
10 may also be implemented in a conventional or non-hybrid vehicle.
A control module 12 controls a fuel injection system 14 with one or
more fuel injectors and an ignition system 16 to selectively
deliver fuel and spark to at least one cylinder 18 of an engine 20.
When fuel and spark are delivered, the engine 20 produces torque
which is transferred by a torque converter 22 and a transmission 24
to a differential 27 and drive-axles 26. Positive drive-axle torque
drives driven wheels 28 of the vehicle. The vehicle may also
include non-driven wheels 30. It is understood that the present
invention may be configured with other driveline component
arrangements. For example, a transaxle may be used.
The control module 12 regulates operation of an electric
motor/generator (EMG) 32. The engine 20 and the EMG 32 are coupled
via a belt-alternator-starter system 34. The EMG 32 may also be
coupled to the engine 20 by a chain drive, a clutch system, or
other device. The EMG functions as a motor by using energy stored
in an energy storage device (ESD) 36 to supplement torque produced
by the engine 20. The EMG 32 may also be driven by the engine 20 to
function as a generator and recharge the ESD 36. In such case, the
EMG 32 produces an electric current which is used to charge the ESD
36. In a conventional powertrain vehicle, torque production is not
supplemented by an electric motor.
The engine 20 may drive an air conditioner (AC) compressor 38
coupled to the engine 20. The air conditioner cools the interior of
the vehicle. The control module 12 controls air conditioner
operation by regulating a capacity or rotational speed of the AC
compressor 38.
The operator presses an accelerator pedal 40 to accelerate the
vehicle. When the operator releases the accelerator pedal 40,
vehicle deceleration may occur. During deceleration, the control
module 12 deactivates fuel delivery to the engine 20 by
deactivating fuel delivery to the at least one cylinder 18. In some
implementations, deactivation is performed by activation and
deactivation of intake and/or exhaust valves. When fuel delivery to
the at least one cylinder 18 is deactivated, the fuel injector for
the cylinder 18 is deactivated and spark is not delivered to the
cylinder 18. When fuel delivery is deactivated, the engine 20 does
not produce torque and may be back-driven by the wheels 28 through
the transmission 24 and torque converter 22. During deceleration,
the EMG 32 and AC compressor 38 may also be back driven. Negative
drive-axle torque results when the engine 20, EMG 32, and AC
compressor 38 are back driven by the wheels 28.
When the operator presses the accelerator pedal 40, positive
drive-axle torque is increased. When the force of the positive
drive-axle torque becomes greater than the frictional force between
the road and the drive wheels 28, positive wheel slip may occur.
The control module 12 receives a traction control signal 42,
indicating whether the traction control system is enabled. The
traction control system may be selectively enabled by a push button
accessible to the operator. The traction control system generally
controls positive wheel slip by decreasing the torque delivered to
slipping wheels. The operator may disable traction control,
however, to drive the vehicle aggressively. In such case the
operator may intentionally induce positive wheel slip.
The control module 12 controls the ignition system 16 and fuel
injection system 14 to deliver spark to the at least one cylinder
of the engine 18. The control module 12 determines a point during a
piston stroke to deliver spark to the cylinder 18. The control
module 12 may deliver spark at an optimal point during the piston
stroke to produce the maximum amount of torque. The control module
12 may also deliver spark at a point after the optimal point. When
spark is delivered after the optimal point, the engine 20 produces
less than the maximum amount of torque. The time interval between
the optimal point and the point at which spark is delivered is the
spark offset. As the spark offset increases, torque production
decreases.
The control module 12 monitors wheel speed signals generated by
wheel speed sensors 44 and calculates vehicle speed based on the
wheel speed signals. The control module 12 includes a slip
detection module (SDM) 46 that receives the wheel speed signals and
that calculates wheel slip as the difference between the wheel
speed of the driven wheels 28 and the wheel speed of the non-driven
wheels 30. The SDM 46 determines when a positive or negative wheel
slip is occurring, or about to occur. As can be appreciated, other
suitable vehicle speed and wheel slip detection means may be
employed to calculate vehicle speed and wheel slip.
The control module 12 monitors torque parameters to develop a model
of torque production and consumption. The control module 12
receives an engine rotational speed signal (ERPM) that is generated
by an engine rotational speed sensor 52 based on a rotational speed
of the engine. Based on ERPM and on the state of the ignition
system 16 and fuel injection system 14 (i.e., whether fuel delivery
is activated or deactivated), the control module 12 determines
whether the engine 20 is currently producing torque or currently
being back driven. Likewise, the control module 12 determines
whether the EMG 32 is currently producing torque or currently being
back driven.
The control module 12 controls a current gear of the transmission
24. The gear ratio determines the amount of torque transferred
between the engine 20 and the drive-axles 26.
The control module 12 controls a capacity of the AC compressor 38.
The AC compressor 38 is driven by the engine. Increased capacity
results in increased torque consumption by the AC compressor 38.
Alternatively, the control module 12 may control a rotational speed
of the AC compressor 38, wherein increased compressor rotational
speed results in greater cooling by the air conditioner.
The control module 12 also monitors a torque converter clutch slip
rate signal (TCC.sub.Slip) that is generated by a torque converter
clutch slip sensor 48. TCC.sub.Slip is the difference between ERPM
and a rotational speed of an output shaft of the torque converter
22. When the engine 20 is providing torque to the transmission 24,
ERPM may be greater than the rotational speed of the output shaft,
resulting in a positive TCC.sub.Slip. When the engine 20 is
back-driven by the transmission 24, the rotational speed of the
output shaft may be greater than ERPM, resulting in a negative
TCC.sub.Slip. Thus, the torque converter clutch slip sensor 48 may
actually be composed of two sensors that monitor the input and
output rotational speeds of the torque converter 22. The TCC slip
sensor 48 may output the difference between the two rotational
speeds. Alternatively, a TCC slip sensor 48 may be replaced with an
output shaft rotational speed sensor. In such an embodiment, the
control module 12 may receive an output shaft rotational speed
signal, and calculate TCC.sub.Slip based on ERPM and the output
shaft rotational speed signal.
Based on ERPM, TCC.sub.Slip, the current transmission gear, the
fuel injection system 14, the ignition system 16, the EMG 32, the
AC compressor capacity, and the wheel speed signals, the control
module 12 determines drive-axle torque. When the EMG 32 and/or the
engine 20 are producing torque, positive drive-axle torque may
result. When the EMG 32 and/or the engine 20 are not producing
torque, and the EMG 32 and/or engine 20 are back-driven, negative
drive-axle torque may result.
The control module 12 includes a torque control module (TCM) 50 to
neutralize negative drive-axle torque. When negative wheel slip
occurs due to increased negative drive-axle torque, the TCM 50
implements a torque control routine to increase the drive-axle
torque. The TCM adjusts the fuel injection system 14, the ignition
system 16, the EMG 32, the AC compressor 38, and the current
transmission gear, to neutralize negative drive-axle torque or to
create a slightly positive drive-axle torque.
Referring now to FIG. 2, steps performed by the control module 12
according to the present invention are illustrated. Control begins
in step 200. In step 202, control determines whether a wheel slip
is detected. As discussed above, the SDM 46 monitors the wheel
speed signals to detect a wheel slip. The SDM 46 may broadcast a
wheel slip signal to the control module 12, including the TCM
50.
When a wheel slip is detected, control proceeds to step 204 and
determines whether the wheel slip is a positive wheel slip or a
negative wheel slip. When the wheel slip is a negative wheel slip,
control proceeds to step 206. The negative wheel slip may be the
result of increased negative drive-axle torque.
In step 206, torque control is enabled. As discussed in more detail
with reference to FIG. 3 below, when torque control is enabled the
TCM 50 executes a torque control routine to neutralize negative
drive-axle torque. To enable torque control, a torque control
enable signal is generated or a torque control enable flag is set.
After enabling torque control in step 206, control proceeds to step
208.
In step 208, control determines whether negative wheel slip
continues to occur. Control loops on step 208 until negative wheel
slip is no longer detected. When negative wheel slip is no longer
detected, control proceeds to step 210.
In step 210, control determines whether a reset period has expired.
The reset period begins when negative wheel slip is no longer
detected. Control loops on steps 208 and 210 until the reset period
expires. When the reset period expires without the detection of
additional negative wheel slip, control proceeds to step 212. When
additional negative wheel slip is detected prior to the expiration
of the reset period, then control loops on step 208 until the
negative wheel slip is no longer detected, and the reset period is
restarted. In this way, torque control is enabled until negative
wheels slip has ceased for the duration of the reset period. The
reset period may be a predetermined period. The reset period may
also be based on the vehicle speed such that higher vehicle speeds
require a shorter reset period.
In step 212, torque control is disabled. To disable torque control,
the torque control enable signal or torque control enable flag may
be reset. When torque control is disabled, control proceeds to step
202.
Referring now to FIG. 3, steps performed by the TCM 50 according to
the present invention are illustrated. Control begins in step 300.
In step 302, control determines whether torque control is enabled.
When torque control is enabled, control enters a torque control
routine 314 and proceeds to step 304.
In step 304, control checks the current torque model parameters
including the EMG 32 torque input or output, AC compressor 38
torque input, the engine 20 torque input or output, the current
transmission gear, TCC.sub.Slip, and the wheel speed signals. Based
on these torque model parameters, control determines the current
drive-axle torque.
In step 306, control calculates adjusted torque model parameters
for neutral or slightly positive drive-axle torque. As discussed
below, in steps 308, 310, and 312, control adjusts the EMG torque,
AC compressor 38, and engine torque based on the calculations of
step 306. After adjusting the torque parameters in steps 308, 310,
and 312, control determines whether torque control remains enabled
in step 302. Control continues to check current torque model
parameters, calculate adjusted torque model parameters, and adjust
torque model parameters, while torque control is enabled.
Initially, in a hybrid vehicle negative drive-axle torque is
neutralized by increased torque produced by the EMG 32. The EMG 32
is switched from a recharging, or torque consuming, mode to a
torque producing mode. A rotational speed of the EMG 32 is set at a
level sufficient to create a neutral, or slightly positive,
drive-axle torque based on the current TCC.sub.Slip and
transmission gear in step 308. In a conventional powertrain
vehicle, torque control is implemented by increasing engine torque
production. In both cases, torque control may also include
decreasing AC compressor 38 capacity or AC compressor 38 rotational
speed.
On subsequent iterations of the torque control routine 314, the TCM
50 coordinates a net-zero, or slightly positive, drive-axle torque,
while the EMG 32, engine 20, and AC compressor torque parameters
are gradually adjusted. In this way, negative drive-axle torque is
neutralized while maintaining drivability.
Fuel delivery to the engine 20 is gradually increased by activating
individual cylinders 18 and skipping a predetermined number of
engine cycles in between cylinder activations. Additionally, the
ignition system 16 may initially be set with a large initial spark
offset. The spark offset may be gradually decreased to increase
torque production of the engine 20. As engine torque production
increases, EMG 32 torque production is decreased. In addition, the
AC compressor capacity may be increased as the engine torque
production is increased.
The coordinated torque control continues until torque control is
disabled. When torque control is disabled, control loops on step
302 until torque control is enabled.
Referring again to FIG. 2, in step 204 when control determines that
the detected wheel slip is a positive wheel slip, control proceeds
to step 214. In step 214, when traction control is enabled, control
loops back to step 202. When traction control is disabled, control
proceeds to step 216.
When traction control is disabled, and a positive wheel slip is
detected, the operator is aggressively driving the vehicle and may
be intentionally inducing positive wheel slip. In such case, the
operator may not desire fuel efficiency functions to be performed.
In step 216, fuel efficiency functions are disabled.
Fuel efficiency functions may include a deceleration fuel
deactivation function and an idle stop function. The deceleration
fuel deactivation function is generally implemented such that fuel
delivery to the engine is deactivated during periods of
deceleration. The idle stop function is generally implemented such
that fuel delivery to the engine is deactivated while the vehicle
is stopped.
Referring now to FIG. 4, and with continued reference to FIG. 2,
steps for disabling fuel efficiency functions are illustrated. It
is understood that the steps illustrated in FIG. 4 are encapsulated
by step 216 of FIG. 2. In step 400, control disables the
deceleration fuel deactivation function. In step 402, control
disables the idle stop function. The fuel efficiency functions may
be disabled by setting, or resetting, corresponding flags or
signals.
Referring again to FIG. 2, after disabling fuel efficiency
functions, control proceeds to step 218. In step 218, control
determines whether a positive wheel slip persists. Control loops on
step 218 while a positive wheel slip continues. When positive wheel
slip terminates, control proceeds to step 220.
In step 220, control determines whether a reset period has expired.
Control loops on steps 218 and 220 until the reset period expires.
When the reset period expires without the detection of additional
positive wheel slip, control proceeds to step 222. When additional
positive wheel slip is detected prior to the expiration of the
reset period, then control loops on step 218 until the positive
wheel slip is no longer detected, and the reset period is
restarted. In this way, fuel efficiency functions remain disabled
until positive wheel slip has ceased for the duration of the reset
period. The reset period may be a predetermined period. The reset
period may also be based on the vehicle speed such that higher
vehicle speeds require a shorter reset period.
In step 222, fuel efficiency functions are enabled. Referring now
to FIG. 5, and with continued reference to FIG. 2, steps for
enabling fuel efficiency functions are illustrated. It is
understood that the steps illustrated in FIG. 5 are encapsulated by
step 222 of FIG. 2. In step 500, control enables the deceleration
fuel deactivation function. In step 502, control enables the idle
stop function. Referring again to FIG. 2, after control enable fuel
efficiency functions, control proceeds to step 202.
A vehicle equipped with the wheel slip control system of the
present invention may also be equipped with an anti-lock braking
system. In such case, the wheel slip control system may operate
independent of the anti-lock braking system. The anti-lock braking
system and the wheel slip control system may share wheel slip
detection functions. With reference to FIG. 1, an anti-lock braking
system may receive wheel slip detection signals from the SDM.
The description of the invention is merely exemplary in nature and,
thus, variations that do not depart from the gist of the invention
are intended to be within the scope of the invention. Such
variations are not to be regarded as a departure from the spirit
and scope of the invention.
* * * * *